Global positioning system (GPS) is well known as an advanced technology that can be use to determine a location of an object on or above the earth. In conventional GPS systems, GPS receivers are attached to objects to track GPS signals and demodulate the GPS signals into GPS navigation messages which can include the satellite clock error, ephemeris, almanac for each satellite in the constellation, and the information about coordinated universal time, etc., and to determine the location of the objects based on the demodulated navigation messages. In addition, the GPS receiver also calculates the GPS time at which the GPS receiver receives the GPS signals according to the demodulated navigation messages. Usually, before tracking and demodulating a GPS signal, the GPS receiver needs to acquire the GPS signal. Thus, the GPS receiver may first need to determine a boundary of a navigation data bit in the GPS signal, e.g., a conventional navigation data bit that is 20 ms long, and then acquire the GPS signal based on a coherent integration process.
When the GPS receiver is powered off, a real time clock (RTC) can be used to provide a local time of the receiver. However, when the GPS receiver is re-powered on after being powered off for a time interval, the local time from the RTC may not be accurate enough to be used to determine the boundary of the navigation data bit in the GPS signal. Thus, the GPS receiver may need to operate the conventional GPS bit synchronization process to determine the boundary of the navigation data bit, which may take a relatively long time.